1. Field of the Invention
One embodiment relates to a photosensitive paste composition, a plasma display panel (hereinafter, referred to as “PDP”) electrode manufactured using the photosensitive paste composition, and a PDP comprising the PDP electrode. More particularly, the present embodiment relates to a photosensitive paste composition that contains conductive powder having an optimized particle diameter and particle diameter distribution to improve electrode characteristics, a PDP electrode manufactured using the photosensitive paste composition, and a PDP comprising the PDP electrode.
2. Description of the Related Art
Recently, various pattern machining techniques have been developed with the increasing need for large, high density, high definition, highly reliable display devices. In addition, compositions for forming various microelectrodes that are compatible with such various pattern machining techniques have been vigorously researched.
PDPs have been used in various fields since PDPs have faster response speed and can be more easily manufactured with a large size compared with liquid crystal panels. In general, patterning electrode materials using screen printing has been used as a conventional method of forming electrodes on a PDP. However, this method requires high proficiency, and patterns for high definition, large screens for PDPs are difficult to be obtained with this conventional screen printing method since this method uses a screen with a low resolution. Furthermore, the conventional screen printing method leads to a short-circuit or disconnection during a printing process due to the use of the screen and limits the resolution. Therefore, it is limited to manufacture micro-electrode patterns using the conventional screen printing method.
Therefore, in recent years, photolithography using photosensitive paste has been developed to form a high resolution electrode pattern suitable for large screens. This photography technique is a method of forming patterned electrodes by coating the entire surface of a substrate, for example, a glass substrate, with a photosensitive paste, drying the substrate under predetermined conditions, exposing the substrate using a UV exposure apparatus with a photomask, performing developing to remove an uncured portion shielded by the photomask using a suitable developing solution, and calcinating the remaining cured layer at a predetermined temperature.
The photosensitive paste contains conductive powder, an inorganic binder, such as glass frits, a copolymer binder, a photoinitiator, and a solvent, etc. The conductive powder is a material for providing conductivity to electrodes. Silver, gold, copper, platinum, palladium, aluminum, an alloy thereof and the like can be used as conductive powder. Among these materials, silver powder is widely used as conductive powder since silver powder has superior conductivity, can be easily processed into fine powder, and has low cost.
In general, silver powder used for PDP electrodes has an average particle diameter of about 0.1 to about 10.0 μm, and a specific surface area of about 0.3 to about 2.0 m2/g. In general, when the average particle diameter is about 1.0 μm, the minimum particle diameter (Dmin) ranges from about 0.1 μm to about 0.3 μm, and the maximum particle diameter (Dmax) ranges from about 6.0 μm to about 8.0 μm. When the average particle diameter is about 2.0 μm, the minimum particle diameter ranges from about 0.3 μm to about 0.5 μm, and the maximum particle diameter (Dmax) ranges from about 8.0 μm to about 10.0 μm. However, Since conventionally used silver powder has a wide particle diameter distribution, it cannot satisfy the requirements for an electrode's main characteristics, for example, in terms of resistance, the anti-sanding property of terminal portions, withstanding voltage characteristics, etc.
In addition, when silver powder has a wide particle diameter distribution, such silver powder contains particles having diameters smaller than about 0.5 μm and larger than about 5.0 μm. In this case, silver particles having diameters smaller than about 0.5 μm lowers the sensitivity to exposure and results in undercuts after a developing process. Also, such small silver particles have strong sintering behavior and lead to serious shrinking during a calcination process. As a result, serious edge curling occurs during the calcination process, thereby deteriorating withstanding voltage characteristics. Meanwhile, silver particles having diameters larger than 5.0 μm degrades the linearity of electrode patterns, and in particular, degrades the density of the electrodes after calcination due to inferior sintering property, thereby raising resistance and causing damage, a detachment or disconnection on terminal portions of the electrodes during a sanding process.